1. Field of the Invention
The present invention relates to an etching apparatus, and more particularly, to an etching apparatus for manufacture of a liquid crystal display (LCD).
2. Description of the Related Art
An LCD uses a liquid crystal screen formed by coupling a first glass substrate having display or switching elements and a second glass substrate having color filters. In order to form such elements on the first glass substrate, metal layers, insulating films, and amorphous silicon layers are deposited on the first glass substrate and are patterned several times. The majority of LCD panels utilize a glass substrate since the glass substrate is transparent, can be processed at a temperature of up to about 400° C., and easily available. However, the glass substrate has a high density and is fragile. In the course of processes described above, the glass substrate is exposed to temperatures that vary from room temperature to 300° C., and accordingly, it may be damaged due to resultant physical and/or thermal stresses.
LCDs should be formed as thin and light as possible, but factors such as described above, limit the thinning of the glass substrate (currently, it is possible to reduce the thickness of a single glass substrate down to 0.7 mm, for example). Further, since the thinning of the glass substrate is more limited as the size of the glass substrate increases, it is very important to solve the problem in view of the current trend of increasing the size of the glass substrate (at present, the size is increased from 300 by 400 mm to 370 by 470 mm, and further, to 550 by 650 mm).
Recently, an alternative approach has been proposed for solving this problem. A thick glass substrate is used at the beginning of the process in order to prevent the substrate from breaking, and then the thick glass substrate is thinned at a later stage. That is, after upper and lower glass substrates are prepared by forming, for example, switching elements and color filters on the respective glass substrates and then sealed to each other, the resultant panel is thinned by removing portions of the outer surfaces of the substrate. Since the above process sequence can decrease the breakage rate of the glass substrates and the defect ratio of the elements, it is possible to improve the production yield of LCDs.
Two methods are available to thin the glass substrate: a method using polishing powder for physically grinding the substrate and a method using acid solutions for etching the substrate.
An etching apparatus for wet etching includes a loader for loading a cassette, in which multiple sealed panels are vertically inserted in the slots therein in order to facilitate transfer of the panel, and an etch bath for use in the etching process of the sealed substrates using an etchant after moving the cassette from the loader to the etch bath. The etching apparatus further has a rinse bath for use in the cleaning process of the substrate after moving the etch-processed cassette from the etch bath to the rinse bath, a dry bath for use in the drying process of the substrate after moving the cleaned cassette from the rinse bath to the dry bath, and an unloader for use in unloading the dried cassette from the dry bath to a site for conveying the substrates to other process apparatus. In the etch apparatus, the transfer of the cassette is automatically performed by an automatic conveying system.
FIG. 1 illustrates a conventional etching apparatus, which shows only an etch bath and parts directly related to the wet etching process of the substrate.
In the conventional etch apparatus as shown in FIG. 1, the etch bath 20 has an inner space in which a cassette can be positioned, and is connected to an etchant diluting tank 12 for supplying an etchant via an etchant inlet pipe 21. A bubble generating plate 27, which generates nitrogen bubbles for uniformly stirring the etchant, is installed at the bottom of the etch bath 20 and connected to a nitrogen supply line 52 via a nitrogen inlet pipe 22.
An HF supply barrel 11 for supplying undiluted HF solution as the etchant is connected to the etchant diluting tank 12 via an undiluted HF inlet pipe 16. Distilled water (D. I. water) supply line 51 is also connected to the etchant diluting tank 12 via a pure water inlet pipe 17.
The outlet pipe 19 of the etchant diluting tank 12 and the outlet pipe 2 of the etch bath 20 are connected to a discharging line 53 for disposing. On/off valves V1, V2, V3, V4, and V5 are installed on the respective inlet pipes and outlet pipes, so that the flow of the fluid including the D. I. water and the etchant can be controlled. A concentration measuring unit 15 is provided for measuring the concentration of the etchant in the etchant diluting tank 12.
The etching process using the conventional etching apparatus above will be explained. First, a cassette is positioned on the loader (not shown). The valve V1 on the undiluted HF solution inlet pipe 22 is opened and then a pump P1 is activated, so that the undiluted HF solution in the HF solution barrel 11 is supplied to the etchant diluting tank 12. At the same time, the valve V3 in the D.I. water inlet pipe 17 is opened to supply the D. I. water in the D. I. water supply line 51 to the etchant diluting tank 12. As a result, the undiluted HF solution is diluted with the D. I. water. At this time, the etchant of a predetermined concentration is prepared by controlling the amounts of both HF solution and D. I. water. The concentration of the etchant prepared is measured by the concentration measuring unit 15 in the etchant diluting tank 12.
When the preparation of the etchant is completed, the supply of the HF solution and D. I. water is stopped, and the valve V2 on the etchant inlet pipe 21 is opened. Then, a pump P2 is activated to fill the etch bath 20 with the etchant. Thereafter, the cassette on the loader is dipped into the etch bath 20 to start the wet etch process of the glass substrates in the cassette. At this time, nitrogen gas is supplied into the etch bath 20 via the bubble generating plate 27 to enhance the etch process. The nitrogen gas is supplied through the bubble generating plate 27 to generate bubbles in the etchant and stir the etchant. The nitrogen gas is continuously supplied to the etchant through the nitrogen inlet pipe 22 connected to the nitrogen supply line 52 so that the stirring of the etchant can be continued throughout the etch process. When the time period set at the etching apparatus for etching the glass substrates is lapsed, the etching process of the glass substrates is stopped. The time period for etching the glass substrates is adjusted in accordance with the concentration of the etchant and the thickness of the glass substrate.
Next, another cassette (not shown), in which the glass substrates are loaded in the slots thereof, is moved into the etch bath, and the same process is performed. Thereafter, the subsequent etching step is performed. The residual etchant used in each etching process is guided into the discharging line 53 through the outlet pipe 2 of the etch bath 20 and then discharged outside.
The glass substrate etched by the etchant is composed of oxides, such as SiO2, BaO, CaO or Al2O3 in its amorphous state, for example. The HF solution used as the etchant dissolves only SiO2, a main component of the glass substrate, when it is reacted with the glass substrate. The corresponding reaction equation is as follows:SiO2+4HF→SiF2↑+2H2OSince the rest of the oxides are not dissolved in the HF etchant, they exist in the etchant in the form of particles. As a result, the residual etchant discharged from the etch bath includes the HF solution of low concentration and many oxide particles resulting from the chemical reaction of the etchant with the SiO2 components of the glass substrates.
The conventional etching apparatus discharges all the residual etchant used in the etching process through the discharging line, and the HF solution included in the residual etchant is not used again. Further, since the improperly handled HF solution may cause pollution, the discharged HF solution needs to be properly disposed. It is desirable that the residual etchant is reused (recycled) to reduce the amount of the residual HF solution to be disposed of.
Furthermore, since in the conventional etching process, the change in concentration of the HF etchant is not considered when determining the etching end point (the etching time was determined by initial etching parameters), the glass substrates are not etched consistently. Since the etching uniformity of the glass substrates depends on the variable concentration of the etchant as well as the thickness of the glass substrate, in order to control the resultant thickness of the glass substrate, it is necessary to correctly measure the HF concentration of the etchant used in the etching process and flexibly adjust the etch time according to the HF concentration. However, it is difficult to measure the HF concentration periodically and correctly. Furthermore, since the conventional etching apparatus cannot be used to etch a large number of glass substrates consistently, it cannot be used for mass production.